Abstract Despite overall declines in the rate of tobacco use in the United States over the past 30 years, nearly 38 million Americans still smoke, posing extremely high risk for long-term health problems and death. There has been extensive research evaluating a wide range of smoking cessation approaches over the past 40 years. Recent reviews note that there has been significant progress in the application of both clinical and public health interventions to help smokers quit; however, they have also concluded that the overall success rate of smokers quitting has not significantly improved. Individual, group and public health interventions ? both with and without adjunctive aids such as nicotine replacement therapy ? have generally used some combination of cognitive-behavioral interventions, but there remains a need for novel, theory-driven approaches to enhance quit rates and innovative interventions that increase reach and engagement, such as those offered via computer or mobile app. We propose to adapt and test the feasibility of a previously piloted cognitive dissonance intervention (CDI) for smoking cessation that will be delivered via a mobile app. Cognitive dissonance interventions have been shown to be successful in treating health-related problems, as well as substance use, and preliminary findings support its use in smoking cessation. The program will be evaluated with 60 adult daily smokers and will be the only cognitive dissonance mobile app for smoking cessation. Our research and development team has extensive experience developing and testing mobile apps and developing and testing cognitive dissonance and smoking cessation interventions. In the first phase, we will use an iterative development plan to design and develop functionality of the first 3 modules of the CDI prototype app. The research team will partner with Twenty Ideas who have extensive experience in the development of mobile apps for smartphones, many of which have been commercialized. We will assess navigation and usability with adult daily smokers. Additional pilot testing will be used to create a prototype version for evaluation. The evaluation study will involve having 60 adults use the app and complete baseline, 1- and 3-month follow-up. Usability data, system log data on program use, and participant satisfaction data will also be analyzed. Input from participants will be gathered to incorporate additional features to be developed during Phase II. Significant changes in quit attempts, number of days without smoking (smokefree days) and changes in smoking attitudes and behavior will be used to determine the efficacy of the Phase I program and evidence for proceeding to Phase II development and evaluation.